1. Field of the Invention
The present invention relates to inkjet recording apparatuses, and more particularly, to an inkjet recording apparatus that can detect defective discharging. Herein, the term “recording” includes applications of ink (printing) to ink support materials such as cloth, strings, paper, and sheet materials. The term “recording apparatus” includes various information apparatuses and printers serving as output devices of the apparatuses.
2. Description of the Related Art
Along with the popularization of information processing apparatuses such as copying machines, word processors, and computers, recording apparatuses (inkjet recording apparatuses) that perform recording with an inkjet recording head have been rapidly popularized as output (recording) apparatuses for the information processing apparatuses.
In general, an inkjet recording apparatus includes a carriage on which a recording head and an ink tank are mounted, a conveying mechanism for conveying a recording medium, and a control circuit for controlling the carriage and the conveying mechanism.
When an ink discharging operation is not performed by the recording head for a long period, the viscosity of ink in an ink passage near a discharge port increases, and the ink is sometimes not discharged normally. Further, if a minute bubble, which grows in the ink in the ink passage for discharging, remains in the ink passage, normal ink discharging is sometimes difficult. This phenomenon of defective discharging due to the remaining bubble pronouncedly appears when the print duty is relatively high. In another case, a bubble enters the ink at a connecting portion of an ink supply passage or an ink supply system, and clogs the ink supply passage. This sometimes hinders normal discharging.
If recording failure is caused by the above-described defective ink discharging, the recording medium is wasted, and the time taken for recording is also wasted. If unclear images are continuously recorded in a so-called “faded recording” state caused immediately before defective discharging occurs, multiple recording media are wasted. Further, if recording is continued in the “faded recording” state, the recording head is heavily loaded, and this sometimes destroys the recording head itself.
In order to avoid the above-described trouble, various defective-discharging detecting devices have been proposed. A typical defective-discharging detecting device is an optical defective-discharging detecting device including a light-emitting portion and a light-receiving portion for receiving light from the light-emitting portion. In this optical defective-discharging detecting device, light from the light-emitting portion is blocked by ink droplets discharged from discharge ports. On the basis of the change in output of the light-receiving portion (change in amount of received light), defective discharging is detected.
Japanese Patent Laid-Open No. 2-194967 discloses an inkjet recording apparatus including an optical defective-discharging detecting device.
FIGS. 16A and 16B explain an operation of detecting defective discharging of ink. FIG. 16A is a schematic view showing a state in which ink discharged from a recording head passes through an optical path between a light-emitting portion and a light-receiving portion, and FIG. 16B is a waveform chart showing an output waveform from the light-receiving portion in this case. FIGS. 17A and 17B also explain an operation of detecting defective discharging of ink. FIG. 17A is a schematic view showing a state in which ink discharging is abnormal, and FIG. 17B is a waveform chart showing an output waveform from the light-receiving portion in this case.
Referring to these figures, a recording head 1 includes a plurality of ink discharge ports 2. Electrothermal transducers (heaters) 3 are provided in the corresponding passages (nozzles) communicating with the ink discharge ports 2. When a discharging pulse (rectangular pulse) for causing ink discharging is applied to an electrothermal transducer 3, ink in the corresponding passage is heated by heat energy from the electrothermal transducer 3. An ink droplet 2005 is thereby discharged from the corresponding ink discharge port 2.
As shown in FIG. 16A, the ink droplet 2005 discharged from an ink discharge port 2 passes through the optical path of light emitted from a light-emitting portion 2001 toward a light-receiving portion 2002. When passing through the optical path, the ink droplet 2005 blocks light from the light-emitting portion 2001, and the amount of light received by the light-receiving portion 2002 is thereby decreased. In this case, the level of an output signal 2006A from the light-receiving portion 2002 is lower than a threshold value 2004, as shown in FIG. 16B.
In contrast, when an ink droplet 2005 is not discharged from an ink discharge port 2, as shown in FIG. 17A, or when an ink droplet 2005 discharged from an ink discharge port 2 is too small, the amount of light received by the light-receiving portion 2002 does not change significantly. In this case, the level of an output signal 2006B from the light-receiving portion 2002 is higher than the threshold value 2004, as shown in FIG. 17B.
When the level of the output signal from the light-receiving portion 2002 is lower than or equal to the threshold value 2004 (the state shown in FIG. 16B), it is determined that the ink discharging operation is normal. In contrast, when the level of the output signal from the light-receiving portion 2002 is higher than the threshold value 2004 (the state shown in FIG. 16B), it is determined that the ink discharging operation is abnormal (defective discharging).
When it is determined that the ink discharging operation is abnormal, a carriage motor is controlled so as to move a carriage, on which the recording head 1 is mounted, to a position where a suction cap is provided. Then, a suction-cap motor is controlled so as to cap the ink discharge ports 2 of the recording head 1 with the suction cap, and ink is sucked from the recording head 1 by a suction pump. As necessary, the carriage motor is controlled so as to move the recording head 1 to a position where a cleaning plate is provided, and the ink discharge ports 2 are cleaned with the cleaning plate.
After ink suction, it is judged again whether the ink discharging operation is normal or abnormal. When it is determined again that the ink discharging operation is abnormal, a message indicating “abnormal” is displayed on a display (for example, an LCD) in the recording apparatus so as to urge the user to refill ink or to replace the recording head. When it is determined that the ink discharging operation is normal, recording is started.
A recording head disclosed in Japanese Patent Laid-Open No. 58-118267 is a liquid discharging device in which a plurality of nozzles are arranged, and in which conductors for detecting the change in temperature are provided in passages (nozzles) between the adjacent electrothermal transducers (beside the electrothermal transducers).
Unfortunately, the above-described inkjet recording apparatus has the following problems.
A plurality of ink droplets are simultaneously discharged from a plurality of discharge ports, and the change in output from the light-receiving portion caused when the ink droplets block the optical path is detected. Therefore, it is difficult to make judgment about defective discharging of ink with respect to each discharge port. It is conceivable to detect the change in output from the light-receiving portion by discharging an ink droplet from only one discharge port. In this case, however, the change in output from the light-receiving portion caused when one ink droplet blocks the optical path is small, and therefore, it is difficult to make an accurate judgment about defective discharging of ink. Further, the optical defective-discharging detecting device is susceptible to external light, which also makes detection of defective discharging difficult. In this way, it is difficult to make an accurate judgment about defective discharging with respect to each discharge port.
Moreover, a defective-discharging detecting operation cannot be performed during recording on a recording medium. For this reason, the user needs to perform a defective-discharging detecting operation before recording on the recording medium in order to check whether ink discharging failure has occurred in the inkjet recording head. This defective-discharging detecting operation decreases the throughput of the recording apparatus.